88 ANNALS NEW YORK ACADEMY OF SCIENCES 



Introduction 



During three years I have carried out some experiments in heredity 

 with mice. My intention was to familiarize myself at first hand with the 

 process of Mendelian inheritance, and for this purpose few groups of 

 animals offer as many advantages as do the races of domesticated mice, 

 not only because of the ease and rapidity with which they breed in con- 

 finement, but also because the relation of the colors has been more fully 

 exploited here than in any other group. The varieties of color also offer 

 an extended field for study. In the course of the work, some crucial 

 experiments bearing on the theory of inheritance of coat color in mice 

 were made, and these are given in the following pages. The discovery 

 of a wild sport of the house mouse led to a study of its inheritance when 

 crossed with domesticated varieties, and the more interesting results of 

 these crosses are here given. Incidentally, I describe some experiments 

 bearing on the theory of the inheritance of acquired characters as tested 

 by artificial waltzers; a few cases of asymmetrical eye color are also de- 

 scribed, and their meaning considered. The occurrence of a second wild 

 sport is briefly mentioned. I have ventured to offer some suggestions 

 concerning the factors involved in heredity of coat color in mice. In 1908 

 I brought forward a tentative hypothesis to account for the segregation of 

 characters in Mendelian inheritance, and I pointed out at the time how 

 this hypothesis might be tested. This test I have now completed, and the 

 evidence that shows that it must be abandoned is here offered for the first 

 time. 



Crosses between a Wild Sport of Mus musculus and Domesticated 



Varieties 



description op the wild sport 



Although many "sports" of wild species have been recorded, there are 

 few cases describing their inheritance when bred either to the typical wild 

 forms from which they arise or to domesticated races of the same species, 

 when such exist. In the summer of 1907, 1 caught in a house at Woods 

 Hole, Mass., a house mouse, Mus musculus, that had a pure white belly, 

 chestnut sides and dark gray back. The mouse had come in from outside, 

 since the house was new and had been closed all winter. Later, I caught 

 two more such mice and, in the same closet, another typical house mouse. 

 In the neighborhood, I have caught a few other white-bellied mice. They 

 must be, therefore, not uncommon in the locality. In 1908, I had sent to 



